CN105698877A - System and method for measuring flow velocity and flow of fluid in pipe - Google Patents

Abstract

The invention discloses a system and method for measuring fluid velocity and flow rate in a pipeline, comprising a pipe joint connected in series in the pipeline, a dynamic pressure sensor is arranged on the outer wall of the pipe joint at a bend, the pipe joint is also connected with a blind pipe, One end of the blind tube connected to the pipe joint is provided with an end plate, and the other end of the blind tube is provided with an end cover, and a piston is arranged inside the blind tube, the piston abuts against the end cover through a spring, and the piston is connected with a displacement sensor through a guide rod The first cavity formed between the end plate and the piston is communicated with the pipe joint through the return pipe; the dynamic pressure sensor and the displacement sensor are respectively connected to the data processing device through the first analog-to-digital converter and the second analog-to-digital converter; The processing device calculates the corresponding flow velocity and flow rate according to the obtained signal, and transmits it to the display for display. The invention can measure the flow velocity and the flow rate of the fluid in the pipeline; it does not affect the circulation of the fluid in the pipeline and has the characteristics of simple structure.

Description

System and method for measuring flow velocity and flow rate of fluid in pipeline

technical field

The invention relates to a metering device, in particular to a system and method for measuring fluid velocity and flow rate in a pipeline.

Background technique

The measurement of fluid pressure, flow velocity and flow rate is very important in many fields. For example, in many industrial processes it is necessary to measure the pressure, flow velocity, flow rate of various pipes in order to properly control the industrial process. Other uses that require fluid measurement include delivering products to customers, such as oil and water.

In the prior art, the flow rate and flow rate of the fluid are mostly measured by the impeller type measuring device, because the time wheel type flow rate and flow measurement device must set the impeller in the pipeline, which affects the flow of the fluid in the pipeline to a certain extent, and the impeller The structure of the type flow velocity and flow measurement device is complex. After long-term use, the impeller is easy to wear and the measurement accuracy is poor.

The invention provides a system and method for measuring fluid flow rate and flow rate in a pipeline, which can measure the corresponding flow rate and flow rate of the fluid by measuring the fluid pressure; it does not affect the flow of the fluid in the pipeline and has the characteristics of simple structure.

Contents of the invention

The object of the present invention is to provide a system and method for measuring the velocity and flow rate of fluid in a pipeline, which can measure the velocity and flow rate of fluid in a pipeline; does not affect the circulation of fluid in the pipeline and has the characteristics of simple structure.

The present invention adopts the following scheme: a system for measuring the velocity and flow rate of fluid in a pipeline, including a pipe joint connected in series in the pipeline. A pressure sensor, the pipe joint is also connected with a blind tube, and the blind tube is located on one side of the dynamic pressure sensor;

One end of the blind pipe connected to the pipe joint is provided with an end plate, the other end of the blind pipe is provided with an end cover, and the end plate is fixedly connected with a return pipe connected with the pipe joint in the direction opposite to the end cover. one end towards the end plate;

The blind tube is provided with a piston, the piston abuts against the end cap through a spring, a guide rod is fixedly connected to one end of the piston close to the end cap, and the guide rod passes through the spring and the end cap successively and is connected with a displacement sensor;

The first cavity formed between the end plate and the piston communicates with the pipe joint through the return pipe;

The dynamic pressure sensor is connected with a first analog-to-digital converter;

The displacement sensor is connected with a second analog-to-digital converter;

The first analog-to-digital converter and the second analog-to-digital converter transmit their respective signals to the data processing device; the data processing device combines the pipe joint parameters, The fluid parameters calculate the corresponding flow rate and flow rate, and then transmit the flow rate and flow rate to the display for display.

The invention measures the dynamic pressure in the pipe joint and the static pressure in the blind pipe, and calculates the flow velocity and flow rate in the pipe joint according to the Bernoulli equation combined with the internal diameter of the pipe joint and the fluid density parameters.

The pipe joint of the present invention adopts an elbow, and the dynamic pressure sensor is used to measure the dynamic pressure of the fluid in the pipe joint; The fluid in the dead leg remains static, so that the piston in the dead leg can only sense the static pressure of the fluid in the dead leg; since the position of the dynamic pressure sensor and the dead leg are basically at the same height, the difference in potential energy is negligible, and the end plate and the piston A variable first cavity is formed between them, and the pipe joint communicates with the variable first cavity through a return-shaped tube. The static pressure on the piston in the first cavity compresses the spring and pushes the displacement sensor through the guide rod, and the piston is subjected to The static pressure becomes the displacement, and the static pressure of the fluid in the dead leg can be calculated through the displacement of the displacement sensor, the elastic coefficient of the spring and the area of the piston.

Many fluids contain impurities. Since the fluid in the dead leg is in a static state, it is easy to deposit for too long, resulting in measurement errors. The above settings are especially suitable for fluids with more impurities. The end cover and the piston can be removed. The blind pipe is cleaned up, and it is not easy to be blocked, and it can also improve the service life of the displacement sensor; the combination of the piston and the spring has a shock absorption effect, which can eliminate the disturbance in the fluid.

The pipe joint and the dynamic pressure sensor are connected by a sealed pipe thread, the outer wall of the dynamic pressure sensor is provided with a first boss in the circumferential direction, and the outer wall of the pipe joint is provided with a second boss corresponding to the first boss; A first sealing ring is arranged between the boss and the second boss;

The blind pipe and the pipe joint are connected by a sealed pipe thread, the outer wall of the blind pipe is provided with a third boss in the circumferential direction, and the outer wall of the pipe joint is provided with a fourth boss corresponding to the third boss. A second sealing ring is arranged between the fourth boss.

When the dynamic pressure sensor is screwed into the pipe joint, the first boss presses the first sealing ring against the second boss to realize double sealing and prevent fluid leakage, and this arrangement facilitates the replacement of the dynamic pressure sensor.

While the blind leg is screwed into the pipe joint, the third boss presses the second sealing ring against the fourth boss to realize double sealing and prevent fluid leakage, and this setting is convenient for removing the dead leg and cleaning it.

The data processing device is connected with an audible and visual alarm device.

When the pressure information obtained by the data processing device is zero, the data processing device controls the sound and light alarm device to give an alarm, so that the monitoring personnel can find out whether the pipeline is damaged.

The outlet of the pipe joint is provided with a switching valve, and the switching valve is a ball valve.

The switch valve can be used as a switch, and the fluid flow will not be affected after the ball valve is fully opened.

The outer circumference of the displacement sensor is connected with the end cover by thread.

Close the switch valve so that the pressure on the dynamic pressure sensor and the piston is equal. Since there is an error between the pressure on the dynamic pressure sensor and the piston, the displacement of the displacement sensor can be adjusted through the thread on the outer circumference of the displacement sensor, so that the pressure on the piston and the pressure on the dynamic pressure sensor can be adjusted. error, so that the measurement is more accurate, and the structure of this adjustment method is simple.

The data processing device is connected with a keyboard.

Since the density of the fluid often has an error with the theoretical density, the measurement accuracy can be improved by measuring the fluid density and correcting it through the keyboard.

The end cover is provided with an air hole, and the second cavity formed between the piston and the end cover communicates with the outside of the blind pipe through the air hole.

The air holes are used for ventilation of the second cavity.

The blind tube and the end cap are connected by threads.

This kind of setting is convenient for cleaning dead pipes and pistons, and is more suitable for fluids that are easy to deposit.

The dynamic pressure sensor is provided with a filter element, which can prolong the service life of the dynamic pressure sensor.

A method for measuring the velocity and flow rate of a fluid in a pipeline is suitable for the above-mentioned system for measuring the velocity and flow rate of a fluid in a pipeline. The key point is that the method includes the following steps:

Step a: the data processing device connects the dynamic pressure sensor to obtain the dynamic pressure in the pipe joint through the first analog-to-digital converter, and stores the pressure value as the first pressure P ₁ ;

Step b: the data processing device obtains the displacement of the piston through the second analog-to-digital converter connected to the displacement sensor, and the data processing device calculates the pressure on the piston through the displacement of the piston, and stores the pressure value as the _second pressure P2;

The data processing device calculates the second pressure P ₂ through the following formula;

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula (1), P ₂ is the pressure that the piston is subjected to, S is the area of the piston, K is the elastic coefficient of the spring, and X is the displacement of the piston;

Step c: the data processing device calculates the pressure difference between the second pressure P ₂ and the first pressure P ₁ ; the absolute value of the pressure difference is set to ΔP; ΔP=|P ₂ −P ₁ |;

Neglecting the potential energy difference between the fluid in the pipe joint and the fluid in the dead leg, according to the Bernoulli equation, the sum of the static pressure energy and the kinetic energy of the fluid in the dead leg should be equal to the sum of the static pressure energy and the kinetic energy of the fluid at the dynamic pressure sensor;

Since the fluid in the dead leg is not flowing, its kinetic energy is zero. The sum of the static pressure energy and kinetic energy of the fluid in the dead leg should be equal to the pressure P ₂ on the piston; the static pressure energy of the fluid in the pipe joint should be equal to the dynamic pressure sensor For the obtained pressure P ₁ , the kinetic energy of the fluid in the pipe joint should be equal to P ₂ -P ₁ ; therefore, the flow velocity V and flow Q at the dynamic pressure sensor can be calculated according to the Bernoulli equation;

Step d: the data processing device (5) calculates the corresponding flow velocity V and flow Q according to the absolute value ΔP of the pressure difference, and the data processing device (5) uses the following formula for calculation;

$\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&times;</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula (2)-(3), V-flow rate, Q-flow rate,

ΔP-the absolute value of the pressure difference, ρ-fluid density, d-the inner diameter of the pipe joint;

Step e: The data processing device sends the flow velocity V and flow Q to the display for display.

The data processing device is connected with an audible and visual alarm device, and when the _second pressure P2 obtained by the data processing device is zero, the audible and visual alarm device is turned on to give an alarm.

Beneficial effects: the invention provides a system and method for measuring fluid velocity and flow rate in a pipeline, which can measure the flow velocity and flow rate of the fluid in the pipeline by measuring the fluid pressure; it does not affect the circulation of the fluid in the pipeline and has the characteristics of a simple structure.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a flow chart of the method of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a system for measuring the velocity and flow rate of fluid in a pipeline includes a pipe joint 1 connected in series in the pipeline, the pipe joint 1 is a right-angle elbow, and the first pipe section 11 of the pipe joint 1 is the inlet of the fluid. The outer wall of the corner of the pipe joint 1 is provided with a dynamic pressure sensor 2, and the pipe joint 1 is also connected with a blind pipe 3, which is located on one side of the dynamic pressure sensor 2; The second pipe section 12 is vertical, which ensures that the blind pipe 3 is perpendicular to the flow direction of the fluid in the pipe joint 1, so that the dead pipe 3 can obtain the static pressure of the fluid.

One end of the blind pipe 3 connected to the pipe joint 1 is provided with an end plate 31, and the other end of the blind pipe 3 is provided with an end cover 32, and the end plate 31 is fixedly connected with a back connected to the pipe joint 1 in the direction facing the end cover 32. Shaped pipe 33, the other end of return-shaped pipe 33 faces end plate 31;

The return pipe 33 is used to reduce the influence of the fluid flow in the pipe joint 1 on the fluid pressure in the blind pipe 3 .

The blind tube 3 is provided with a piston 34, the piston 34 abuts against the end cap 32 through the spring 35, the end of the piston 34 close to the end cap 32 is fixedly connected with a guide rod 36, and the guide rod 36 passes through the spring 34 and the end cap 32 successively. A displacement sensor 4 is connected to the rear; the first cavity 37 formed between the end plate 31 and the piston 34 communicates with the pipe joint 1 through the return pipe 33;

The blind pipe 3 at the right end of the return-shaped pipe 33 is provided with a piston 34, the piston 34 divides the blind pipe 3 into two cavities, the first cavity 37 on the left communicates with the pipe joint 1 through the return-shaped pipe 33, and the third cavity on the right The second cavity 40 communicates with the atmosphere outside the blind pipe 3 . The fluid applies pressure to the piston 34, and the piston 34 changes the pressure received by the piston 34 into displacement through the spring 35 and the guide rod 36.

The dynamic pressure sensor 2 is connected with a first analog-to-digital converter 8;

The displacement sensor 4 is connected with a second analog-to-digital converter 9;

The first analog-to-digital converter 8 and the second analog-to-digital converter 9 transmit respective output signals to the data processing device 5; signal, and combine the parameters of the pipe joint 1 and the fluid parameters to calculate the corresponding flow rate and flow rate, and then transmit the flow rate and flow rate to the display 6 for display.

The pipe joint 1 and the dynamic pressure sensor 2 are connected by sealed pipe threads, the front end of the dynamic pressure sensor 2 is provided with a filter element 21, the outer wall of the dynamic pressure sensor 2 is circumferentially provided with a first boss 22, and the outer wall of the pipe joint 1 is provided with There is a second boss 13 corresponding to the first boss 22; a first sealing ring 23 is arranged between the first boss 22 and the second boss 13;

The blind pipe 3 and the pipe joint 1 are connected by a sealed pipe thread, the outer wall of the blind pipe 3 is provided with a third boss 38 in the circumferential direction, and the outer wall of the pipe joint 1 is provided with a fourth boss corresponding to the third boss 38 14 . A second sealing ring 39 is provided between the third boss 38 and the fourth boss 14 .

The data processing device 5 is connected with an audible and visual alarm device 7 .

The outlet of the pipe joint 1 is provided with a switch valve 10 .

The outer circumference of the displacement sensor 4 is threadedly connected to the end cover 32 .

The data processing device 5 is connected with a keyboard 5a.

The end cover 32 is provided with an air hole 32a, and the second cavity 40 formed between the piston 34 and the end cover 32 communicates with the outside of the blind pipe 3 through the air hole 32a.

Blind tube 3 and end cap 32 are threaded.

As shown in Figure 2, a method for measuring the velocity and flow rate of fluid in a pipeline is suitable for the above-mentioned system for measuring the velocity and flow rate of fluid in a pipeline. The key point is that the method includes the following steps:

Step a: The data processing device 5 connects the dynamic pressure sensor 2 through the first analog-to-digital converter 8 to obtain the dynamic pressure in the pipe joint 1, and stores the pressure value as the first pressure P ₁ ;

Step b: the data processing device 5 connects the displacement sensor 4 to obtain the displacement of the piston 34 through the second analog-to-digital converter 9, and the data processing device 5 calculates the pressure received by the piston 34 through the displacement of the piston 34, and stores the pressure value as the second pressure P2 _;

The data processing device 5 calculates the second pressure P ₂ through the following formula;

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), P ₂ is the pressure that piston 34 is subjected to, and S is the area of piston 34, and K is the elastic coefficient of spring 35, and X is the displacement of piston 34;

Step c: the data processing device 5 calculates the pressure difference between the second pressure P ₂ and the first pressure P ₁ ; the absolute value of the pressure difference is set to ΔP, ΔP=|P ₂ −P ₁ |;

Step d: the data processing device (5) calculates the corresponding flow velocity V and flow Q according to the absolute value ΔP of the pressure difference, and the data processing device (5) uses the following formula for calculation;

$\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&times;</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In formula (2)-(3), V-flow rate, Q-flow rate,

ΔP-the absolute value of the pressure difference, ρ-fluid density, d-the inner diameter of the pipe joint 1;

Step e: The data processing device 5 sends the flow velocity V and flow Q to the display 6 for display.

The data processing device 5 is connected with an audible and visual alarm device 7, and when the second pressure P2 obtained by the data processing device ₅ is zero, the audible and visual alarm device 7 is turned on to give an alarm.

Claims (10)

1. A system for measuring fluid velocity and flow rate in a pipeline, comprising a pipe joint (1) connected in series in the pipeline, the pipe joint (1) is an elbow, characterized in that: the elbow of the pipe joint (1) The outer wall is provided with a dynamic pressure sensor (2), and the pipe joint (1) is also connected with a blind tube (3), and the blind tube (3) is located on one side of the dynamic pressure sensor (2); One end that this blind pipe (3) is connected with pipe joint (1) is provided with end plate (31), and the other end of this blind pipe (3) is provided with end cover (32), and end plate (31) is facing end cover ( 32) is fixedly connected with a return-shaped pipe (33) connected to the pipe joint (1), and the other end of the return-shaped pipe (33) faces the end plate (31); The blind tube (3) is provided with a piston (34), the piston (34) abuts against the end cover (32) through a spring (35), and the end of the piston (34) close to the end cover (32) is fixedly connected with a guide rod (36), the guide rod (36) passes through the spring (35), the end cover (32) successively and is connected with a displacement sensor (4); The first cavity (37) formed between the end plate (31) and the piston (34) communicates with the pipe joint (1) through the return pipe (33); The dynamic pressure sensor (2) is connected with a first analog-to-digital converter (8); The displacement sensor (4) is connected with a second analog-to-digital converter (9); The first analog-to-digital converter (8) and the second analog-to-digital converter (9) transmit respective signals to the data processing device (5); the data processing device (5) according to the first analog-to-digital converter (8) and the second Two, the output signal of the analog-to-digital converter (9), combined with the parameters of the pipe joint (1) and the fluid parameters to calculate the corresponding flow velocity and flow rate, and then transmit the flow velocity and flow rate to the display (6) for display. 2. A system for measuring fluid velocity and flow rate in a pipeline according to claim 1, characterized in that: the pipe joint (1) and the dynamic pressure sensor (2) are connected by a sealed pipe thread, and the dynamic pressure sensor (2) The outer wall is circumferentially provided with a first boss (22), and the outer wall of the pipe joint (1) is provided with a second boss (13) corresponding to the first boss (22); between the first boss (22) and A first sealing ring (23) is arranged between the second bosses (13); The blind pipe (3) and the pipe joint (1) are connected by a sealed pipe thread, the outer wall of the blind pipe (3) is provided with a third boss (38) in the circumferential direction, and the outer wall of the pipe joint (1) is provided with a The fourth boss (14) corresponding to the three bosses (38) is provided with a second sealing ring (39) between the third boss (38) and the fourth boss (14). 3. A system for measuring flow velocity and flow rate of fluid in a pipeline according to claim 1, characterized in that: said data processing device (5) is connected with an audible and visual alarm device (7). 4. A system for measuring fluid velocity and flow rate in a pipeline according to claim 1, characterized in that: the outlet of the pipe joint (1) is provided with an on-off valve (10), and the on-off valve (10) is a ball valve . 5. A system for measuring fluid velocity and flow rate in a pipeline according to claim 1, characterized in that: the outer circumference of the displacement sensor (4) is threadedly connected to the end cap (32). 6. A system for measuring flow velocity and flow rate of fluid in a pipeline according to claim 1, characterized in that: said data processing device (5) is connected with a keyboard (5a). 7. A system for measuring fluid velocity and flow rate in a pipeline according to claim 1, characterized in that: the end cover (32) is provided with an air hole (32a), and the first hole (32a) formed between the piston (34) and the end cover (32) The two cavities (40) communicate with the outside of the blind pipe (3) through the air hole (32a). 8. A system for measuring fluid velocity and flow rate in a pipeline according to claim 1, characterized in that: the blind pipe (3) and the end cap (32) are connected by threads. 9. A method for measuring the velocity and flow rate of a fluid in a pipeline, suitable for a system for measuring the velocity and flow rate of a fluid in a pipeline according to claim 1, characterized in that the method comprises the following steps: Step a: the data processing device (5) connects the dynamic pressure sensor (2) through the first analog-to-digital converter (8) to obtain the dynamic pressure in the pipe joint (1), and stores the pressure value as the _first pressure P1; Step b: the data processing device (5) connects the displacement sensor (4) to obtain the displacement of the piston (34) through the second analog-to-digital converter (9), and the data processing device (5) calculates the displacement of the piston (34) by the displacement of the piston (34). ) is subject to the pressure, and store the pressure value as the second pressure P ₂ ; The data processing device (5) calculates the second pressure P2 by the following _formula ; ${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ In formula (1), P ₂ is the pressure that piston (34) is subjected to, and S is the area of piston (34), and K is the elastic constant of spring (35), and X is the displacement of piston (34); Step c: the data processing device (5) calculates the pressure difference between the second pressure P ₂ and the first pressure P ₁ ; the absolute value of the pressure difference is set to ΔP; ΔP=|P ₂ −P ₁ |; Step d: the data processing device (5) calculates the corresponding flow velocity V and flow Q according to the absolute value ΔP of the pressure difference, and the data processing device (5) uses the following formula for calculation; $\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ $\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&times;</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ In formula (2)-(3), V-flow rate, Q-flow rate, ΔP-the absolute value of pressure difference, ρ-fluid density, d-pipe joint (1) inner diameter; Step e: The data processing device (5) sends the flow velocity V and flow Q to the display (6) for display. 10. A method for measuring fluid velocity and flow rate in a pipeline according to claim 9, characterized in that: said data processing device (5) is connected with an audible and visual alarm device (7), when the data processing device (5) When the _second pressure P2 is zero, the sound and light alarm device (7) is connected to report to the police.